Electric valve circuit



April 10, 1934.

His Attomeg Patented Apr. 10, 1934 UNITED STATES ELECTRIC VALVE CIRCUITMarvin M. Morack, Schenectady, N. Y., assignor to General ElectricCompany, a corporation of New York Application January. 10, 1931, SerialNo. 507,908

14 Claims.

My invention relates to electric valve circuits and more particularly tosuch circuits including valves of the thermionic cathode type.

In the operation of electric valves of the thermionic cathode type,such, for example, as those having incandescent cathodes or thoseprovided with el'ectron emitting cathodes heated from an independentheater, it is essential to the satisfactory operation of the valves thatthe cathodes shall have reached their normal operating temperaturebefore the valves are energized to carry the current of the'translatingcircuit in which they are connected and that the current in the valvesshould be interrupted in case their cathodes drop substantially belowtheir normal operating temperature. This is especially true in the caseof electric valves of the vapor electric discharge type which relyprimarily for their operation upon the ionization of the containedvapor. If a valve of this type is energized to carry the current of atranslating circuit before its cathode reaches its proper temperature, alarge part of the potential of the translating circuit will be consumedin the valve, the effect of which is to destroy the electron emittingproperties of the cathode by positive ion bombardment. In a copendingapplication of Alan S. Fitz Gerald Serial No. 507,906, led January 10,1931, and assigned to the same assignee as the present application,there is disclosed an arrangement for preventing the operation of anelectric valve in a translating circuit whenever the cathode is belownormal operating temperature. Accordingr to the arrangement disclosed inthat application the electric valve is disconnected from the translatingcircuit whenever its cathode is below its normal operating temperature.My invention relates more specifically to electric valve circuitsl ofthis type and constitutes an improvement upon the arrangement disclosedin the above-mentioned application.

It is an object of my invention to provide an improved electrictranslating circuit including an electric valve of the thermioniccathode type in which the ilow of current in the valve will be delayeduntil the cathode reaches substantially its operating temperature and inwhich this result is accomplished without the use of contacts in thetranslating circuit. It is another object of my invention to provide animproved electric translating circuit including an electric valve of thethermionic cathode type in which the valve is maintained non-conductiveupon initiation of the operation of the apparatus until the cathodereaches substantially its normal operating tem- (Cl. Z-27) perature. Itis a further object of my invention to provide an improved electrictranslating circuit including an electric valve of the thermioniccathode type in which a thermal responsive means independent of theelectric valves but having thermal characteristics similar to those ofsaid cathode, acts to maintain the valve non-conducting uponenergization of the translating circuit until the cathode of the valvereaches substantially its normal operating temperature.

In accordance with my invention I provide a thermal responsive meanssuch as a thermostatic relay or a thermal resistance bridge which isenergized in accordance with the energizaticn of the heating circuit forthe thermionic cathode.

This thermal responsive device is designed to have thermalcharacteristics similar to those of the thermionic cathode; that is, itwill reach the temperature at which a desired operation is produced atsubstantially the same time the thermionic cathode reaches its normaloperating temperature although these operating temperatures may bewidely different. The electric valve is pro-- vided with a control gridthe excitation of which is controlled by the thermal responsive means tomaintain the valve non-conducting until its cathode reaches its propertemperature.

For a better understanding of my invention together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims. In Fig. 1 of the accompanyingdrawing I have illustrated my invention as applied to an arrangement fordelaying the time at which the electric valvesl ol a controlledrectifier are made conducting until their cathodes reach their propertemperature; Fig, 2 illustrates a modication of my inventioninvolving adiiferent type of thermal responsive means and grid control, while Fig.3 illustrates an embodiment of my invention as applied to a parallelinverter, i. e. an apparatus for converting direct current intoalternating current.

Referring more particularly to Fig. 1 of the accompanying drawing, Ihave illustrated a translating circuit for receiving alternating currentfrom the supply circuit 10, converting it into direct current, anddelivering it to the receiving circuit 11. This translating circuitcomprises a transformer 12, and electric valves 13 and 14 each providedwith an anode, a control grid and a thermionic cathode. The valves 13and 14 may be of any of the several types well known in the art althoughI prefer to use valves of the vapor electric discharge type. The valves13 and 14 are provided with independent cathode heaters 15 and 16respectively, energized from the secondary winding 17 of a transformer18, the primary winding ofwhich is connected across the alternatingcurrent circuit. The grids of electric valves 13 and 14 are connected tothe common cathode connection through opposite halves of the secondarywinding of a grid transformer 19 and a negative bias battery 20. Inorderto control thegrid potential of valves-l3 and 14 1 have provided athermal responsive bridge cornprising resistors 21 and 22 which make upone pair of opposite arms of the bridge and resistors 23 and 24 whichconstitute the other arms. Resistors 21 and 22 and 23 and .24 havedissimilar temperature-resistance characteristics. For example,resistors 21 and 22 may have substantially zero temperature-resistancecharacteristics while one or both of resistors 23 and 24 may have highlypositive temperature resistance characteristics and preferably havethermal characteristics similar to those of the cathodes of electricvalves 13 and 14. One diagonal of the bridge is energized from asecondary winding 25 of the trans-v former 18 while the other diagonalof the bridge is connected to the primary winding of grid transformer19.

The general operation of a full wave rectier such as that comprisingtransformer 12 and electric valves 13 and 14 is so well understood bythose skilled in the art that the explanation of the operation of theabove described apparatus will be conned to the control or' the gridpotentials of electric valves 13 and 14. When the circuit 10 is rstenergized sothat the temperatures of the several resistors making up thethermal bridge are at the ambient temperature, the bridge is soproportioned that the potential of the diagonal connected to the primarywinding 'of the grid transformer 19 is zero so that no potential will beimpressed upon the grids of the valves 13 and 14 from the transformer 19and each of these grids will have a negative bias derived from thebattery 20, i. e. both valves 13 and 14 are nonconducting. At the sametime current is supplied from the secondary winding 17 to the heaters 15and 16 of electric valves -13 and 14. As the temperature of the cathodeheaters rises, the temperature of' the, resistors 23 and 24 of thethermal bridge will increase proportionally so as to unbalance thethermal bridge. The unbalanced potential of the thermal bridge is nowimpressed upon the primary windingl of the grid transformer 19 which isso connected that this potential opposes the negative bias of thebattery 20 and is suicient in magnitude to substantially overcome it.When the resistors 23 and 24 reach a temperature corresponding to thenormal operating temperature of the cathodes of the valves, although, asstated above, these temperatures need not be the same. The

` result is that an alternating potential in phase Cuit 11.

with the anode potential of electric valves 13 and 14 is impressed upontheir grids and these valves are each rendered conducting during theirrespective positive half cycles of anode potential to deliver their fulloutput to the receiving cir- It will be apparent that, should the sourceof heating current be interrupted by fallure of the transformer 18,deenergization of the circuit 10, or for any other cause, the reverseoperation will take place, the resistors 23 and 24 cooling in accordancewith cathode heaters 15V and 16, the balance of the thermal bridge beingrestored and the negative bias battery 20 again rendering the valves 13and 14 non-conducting.

In the modification of my invention illustrated in Fig. 2, the gridpotentials of the valves 13 and 14 are controlled by animpedance phaseshifting circuit. This phase shifting circuit comprises a reactor 30provided with an electrical -mid-point and energized directly across thesecondary winding 25 of the transformer 18, a capacitorv 31 and aresistor 32, provided with an intermediate tap 33. In order to controlthe portion of the resistor which is eiective in the phase shiftingcircuit, there is provided a thermostatic relay 34 provided with anindependent heater 35 also connected directly across the secondarywinding 25. The operation of this arrangement is similar to thatdescribed above in connection with Fig. 1. The heater 35 ha's thermalcharacteristics similar to those of the cathode heaters 15 and 16, andwhen it arrives at a temperature corresponding to the normal temperatureof the heaters 15 and 16the thermostatic relay 34 operates to shortcricuit a portion of the resistor through the tap 33. The phase shiftingcircuit is normally so proportioned that the potential applied to thegrid transformer 19 is in phase opposition to thel anode potentials orelectric valves 13 and 14. When the relay 34 operates, however, theresistance of resistor 32 is reduced to a very small value with theresult that the grid potential is advanced approximately 180 degrees andis substantially in phase with the anode potentials of the valves 13 and14. With this arrangement electric valves 13 and 14 are fully conductiveduring their respective half -cycles of positive anode potential as inthe' arrangementillustrated in Fig. 1.

In Fig. 3 1 have illustrated a modication for delaying the ow of currentin an electric valve connectedin a translating circuit for receivingenergy from the direct current circuit 11, converting it intoalternating current, and delivering it to receiving circuit l0. Thiscircuit is of the type known in the art as a parallel inverter andcomprises a transformer 12 provided with a 120 primary winding having anelectrical mid-point, the two halves of the primary winding beingconnected across the direct current circuit 11 through a pair ofelectric valves 13 and 14. A capacitor 40 is connected between anodecircuits 125 of the valves 13 and 14 in order to facilitate the transferof current between them. The grids of the valves 13 and 14 are connectedto a common cathode circuit through opposite halves of the secondarywinding of a grid transformer 41A and 3130 a capacitor 42. The primaryvwinding of the grid transformer 41 is energized from the alternatingcurrent circuit, illustrated in the drawing as a half of the secondarywinding of transformer 12 through a capacitor 43, which together withcapacitorii), aids in determining the frequency of the alternatingcurrentl delivered to the power transformer 12. The cathode heaters 15and 16 of the valves 13 and 14, respectively, may be energized byconnecting them directly across the direct current circuit 11. In orderto delay'the ow of current in valves 13 and 14 until their cathodesreach the proper operating temperature, there is provided a thermostaticrelay 34, having an independent heater 35 connected across the directcurrent circuit 11. As in the arrangement described above, the heater 35has thermal characteristics similar to those of the cathode heaters 15and 16. Upon operation of the thermostatic relay 34, the grids of thevalves 13 and 14 are 150 connected directlyto the positive directcurrent i line 11 through a resistor 44.

The general principles of operation of a trans- -lating circuit forconverting direct current into alternating current will be wellunderstood by those skilled in the art, or may be found described inmore detail in United States Letters Patent No. 1,800,002, granted April7, 1931 upon the application of E. F. W. Alexanderson. In brief, ifelectric valve 13 is first made conducting, current will first iiowthrough the left-hand portion of the primary winding of transformer l2and electric valve 13, at the same time inducing a half wave ofalternating potential in the secondary winding of ltransformer 12. Whenelectric valve 14 is made conducting, capacitor40 tends to dischargethrough the valves 13 and 14 in series,'interrupting the current invalve 13. Current now flows through the right hand portion of theprimary winding of-,transformer 12 and electric valve 14, inducing ahalf cycle of opposite polarity in the secondary winding of transformer12, and this cycle is repeated indefinitely, the frequencybeingdetermined by the reactive constants of the circuit. It will benoticed that, when no current is ilowing in the translating circuit, thegrids of the valves 13 and 14 are insulated from their cathodes by thecapacitor 42. These valves lpreferably have positive critical gridpotential characteristics, i. e. valves of the type in which currentcannot be initiated through the valves unless thegrid potential ispositive. However, if valves having negative critical grid potentialcharacteristics are used, the same effect may be obtained by including anegative bias battery in the grid circuit.. With thisA arrangement, bothvalves are maintained non-conducting upon,

energizationof the direct current circuit 11. However, as the cathodeheaters 15 and 16 reach the normal operating temperature, the .heater 35will also increase its temperature to operate the thermostatic relay 34and to shock the grids of the valves 13 and 14 withna positivepotential. The value of the resistance 44 may be very high so as not tointerfere with the normal operation of the apparatus described above, orany well known means may be provided for disconnecting the thermal relay34 upon the initiation of the flow of current through the translatingcircuit.

' While I-have described what I at present consider the preferred.embodiment of my invention, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom my invention, and I FII therefore aim in the appended claims ltocover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the'United States is:-

l. In combination, an electric translating circuit including an electricvalve provided with a thermionic cathode, and means for maintaining saidvalve-non-conductive after the energization Voi' said circuit for a timesuiilcient for said cathode to reach substantially its normal operatingtemperature. Y

2. In combination, an electric translating circuit including an electricvalve provided with a thermionic cathode anda control grid, and meansfor maintaining the potential of saidgrid below its critical valuewhenever the energization of said cathode is below a predeterminedvalue.

3. In combination,l an electric translating cir- I cuit including anelectric valve provided with a thermionic cathode and a control grid,and

means for maintaining said grid below its critical potential for asuiilcient interval after the energization of said circuit for saidcathode to reach substantially its normal operating temperature.

4. In combination, an electrictranslating circuit including an electricvalve provided with a thermionic cathode. and means having thermalcharacteristics similar to those of said cathode for maintaining saidvalve non-conductive for a suiilcient interval of time after theenergization of said circuit for said cathode to reach substantially itsnormal operating,temperature.

5. In combination, lan electric translating circuit including anelectric valve provided with a thermionic cathode, and thermal meansenergized from said circuit and having thermal characteristics similarto those of said cathode for maintaining said valve non-conductive, uponthe energization of said circuit, until said cathode reachessubstantially its normal operating temperature.

6. In combination, an alternating current translating circuit includingan electric valve provided with an anode, a thermionic cathode and acontrol grid, a grid circuit energized from said translating circuit,and means for maintaining said grid potential substantially in phaseopposition t o the potential of said anode until said cathode reachessubstantially its normal operating temperature.

7. In combination, an alternating current translating circuit includingan electric valve provided with an anode, a thermionic cathode and acontrol grid, a grid circuit including a source of 'alternatingpotential oi the same frequency as that of said translating circuit,land a source of negative bias potential, and means associated with saidgrid circuit for maintaining said alternating grid potentialsubstantially in phase opposition to the potential of said anode untilsaid cathode reaches substantially its normal operating temperature.

8. In combination, an electric translating circuit including an electricvalve provided with'a thermionic cathode, .a resistance bridge energizedfrom said circuit, one of the elements of said bridge having thermalcharacteristics similar to those of said cathode, and means responsiveto the balance of saidA bridge for controlling the conductivity of saidvalve.

9. In combination, an electric translating circuit including an electricvalve provided with a thermionic cathode and a control grid, aresistance bridge energized from said circuit, one of the elements ofsaid bridge having theril characteristics similar to those of said cate, and a grid circuit for said valve connected across a diagonal, ofsaid bridgev and including a' source of negative bias potential.

10. In combination, an electric translating circuit including anelectric valve provided with a thermionic cathode, an impedance phaseshifting circuit energized from said translating circuit, thermal meansalso energized from said translating circuit for controlling theconstants of said impedance circuit, and a grid circuit for said valveenergized' from said impedance circuit.

1l. In combination an electric translating circuit including an electricvalve provided with a thermionic cathode, an impedance phase shiftingcircuit energized from said translating cirv the elements of saidimpedance circuit being controlled by said relay, and a grid circuit forsaid valve energized from said impedance circuit.

12. In combination, an electric translating circuitincluding an electricvalve provided with a thermionic cathode and a control grid, and athermal relay having thermal characteristics similar to those of saidcathode and energized from said circuitv and connected to impress apositive impulse upon said grid when in operative posi'- tion.

13. In combination, an alternating current supply circuit, a loadcircuit, an electric VValve provided with a thermionic cathode fortransmitting energy therebetween, and means for mainsubstantially itsnormal operating temperature.-

MARVIN M. MORACK.

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